A major developmental focus of the Human Islet Research Network and Consortium on Modeling Autoimmune Interactions (HIRN-CMAI) is to generate 'humanized' mouse models suitable for studying human autoreactivity in vivo. This is a challenging and ongoing goal of many research groups, including those at our own Center. We perceive that one key current limitation of such animal models is the ambiguity in defining the specificity and function of defined human autoreactive T cell receptors (TCR). Over several years, a number of investigators have isolated a variety of candidate human autoreactive T cell lines and clones derived from T1D subjects. However, the direct role of these differing self-antigen specific T cells in mediating islet beta cell injury remains poorly understood. Therefore, our group proposes to develop a comprehensive program to introduce a series of human autoreactive TCRs into suitable human HLA mouse models to interrogate autoreactivity in vivo. To this end, we have developed collaborations from several investigators world wide to amass a number of islet-reactive T cells from which to harvest human autoreactive TCRs genetic sequences. Our goal is to translate these candidate human TCRs into reproducible animal models by merging three major areas of expertise at our Institution: 1) Expertise in studying human autoreactivity in T1D, 2) Expertise in TCR structure and function and the introduction of TCR gene sequences into animals using 'retrogenic' technology, and 3) Extensive experience in small animal modeling to study T cell reactivity to both native and transplanted islets in vivo. This program is founded on the following Specific Aims: Specific Aim 1: Characterize and evaluate candidate islet antigen- specific CD4 T cells reactive to target human islet cells in vitr. Specific Aim 2: Create 'retrogenic' animal models with T cell receptors (TCR) of a defined antigen specificity and MHC class II restriction. Specific Aim 3: Taken together, the generation of humanized mouse models to reproducibly study autoimmune T1D is an ongoing major challenge currently being addressed by many groups. As such, the key benefits of this developmental program to the HIRN-CMAI are to: 1) Prioritize relevant, pathogenic human TCRs as a platform for studying defined, islet-specific T cells in vivo, 2) Provide a key resource for future introduction of human autoreactive TCRs into human hematopoietic stem in overtly humanized mouse models, 3) Provide a means of testing current and future surrogate islet tissues (e.g., iPS cells) for detection by human autoreactive TCRs, and 4) Provide a platform for testing antigen-specific therapies directed against human T cell autoreactivity in vivo.